Roofing Materials and Methods FAQ
What is the best asphalt shingle to use on my roof?
There are two kinds of asphalt shingles (based on the type of reinforcement mat used): fiberglass and organic. Fiberglass shingles are more fire- and moisture-resistant than organic shingles. Organic shingles have good wind resistance, high tear strength and can be installed in colder temperatures.
Asphalt shingles should be in compliance with American Society for Testing and Materials (ASTM) standards and applicable building codes. Fiberglass shingles should meet ASTM D 3462, “Standard Specification for Asphalt Shingles Made from Glass Felt and Surfaced with Mineral Granules,” and organic shingles should meet ASTM D 225, “Standard Specification for Asphalt Shingles (Organic Felt) and Surfaced with Mineral Granules.”
One contractor’s bid includes 15# underlayment and another contractor says he only uses 30# because it’s the best. Who is right?
For asphalt shingles, NRCA recommends a single layer of 15# asphalt-saturated underlayment be used with roofs having slopes of 4:12 (18 degrees) or greater. For roof slopes between 3:12 (14 degrees) to 4:12 (18 degrees), NRCA recommends a minimum of two layers of 15# underlayment. If you are installing a heavier-weight shingle with a projected long service life, using 30# underlayment instead of 15# would be appropriate.
Are two layers of 15# underlayment the same as one layer of 30# underlayment?
No. Two layers of underlayment are referred to as a “double-layer of underlayment” and there is a 19-inch overlap between layers. One layer of underlayment is called a “single-layer of underlayment” and there is 2 inches of overlap between layers. NRCA recommends a double-layer of underlayment for roof decks having slopes of 3:12 (14 degrees) up to 4:12 (18 degrees).
My contractor wants to use staples instead of nails to install my asphalt shingles. Is that okay?
NRCA recommends galvanized steel or the equivalent corrosion-resistant roofing nails for asphalt shingle installation. Also, verify the governing building code requirements and what the shingle manufacturer recommends.
My contractor suggested installing a ridge vent on my roof and I already have two single static vents. Do I really need a ridge vent?
NRCA suggests the amount of attic ventilation be balanced between the eaves and ridge. The intent of a balanced ventilation system is to provide nearly equivalent amounts of ventilation area at the eave/soffit and at or near the ridge. For a balanced ventilation system to function properly, approximately one-half of the ventilation area must be at or near the ridge.
Proper attic ventilation is one of the least understood concepts in residential roofing. To learn more, read “Principles of Attic Ventilation” an article by Mark Graham, NRCA Associate Executive Director of Technical Services, that appeared in NRCA’s magazine, Professional Roofing or see Technical Bulletin 98-2.
My house has a roof with a 2 1/2:12 (11 degrees) slope. The manufacturer says it’s okay to use asphalt shingles, but my contractor says it isn’t. Who’s right?
There are some manufacturers (and even model building codes) that will allow the application of asphalt shingle roof having that slope; however, NRCA does not recommend shingles on slopes less than 4:12 (18 degrees). Asphalt shingle roof systems are watershedding and rely on gravity and roof slope to effectively drain water off the roof.
My house has a flat roof. What is the best roof system for a flat roof?
There is no one roof system that is best for all applications. Keep in mind that even if you are using the best materials, your roof system still can be installed improperly and you could end up with a leaky roof. Good workmanship and proper attention to detail (e.g., flashing and drainage issues) are just as important as material selection. Also, maintenance plays an important role in roof system integrity and service life.
To assist you in your decision-making, homeowners should be informed of what is available. Please refer to the Roof System Types page to learn about the different low-slope roof systems.